This invention relates generally to draw works and more particularly, but not by way of limitation, to a draw works having a drum shaft supported at four points in association with side plates connected to support members extending transversely to the shaft.
In drilling an oil or gas well, a draw works is needed for providing power to the rotary table and for lowering and lifting pipe strings into and out of the hole. The standard design for a draw works used in this manner has not substantially changed over the years. The standard design includes a shaft which is simply supported by a single bearing on either side of a drum mounted on the shaft. This type of standard design creates cantilevered portions of the shaft extending beyond each of the bearings. To each of these cantilevered portions of the shaft are mounted sprockets for coupling with a variable speed transmission and sprockets for coupling with and providing power to the rotary table and the cat shaft which is used in making and breaking connections between sections of a pipe string as it is lowered into or lifted out of the well hole. An example of this type of draw works is the National 80-B consolidated rig marketed by the National Supply Company.
A shortcoming of this construction is that each end of the shaft is in effect a simply supported beam. Being simply supported permits the shaft to be deflected a relatively large amount by the action of the drum mounted on the shaft and the weight of the cable wound on the drum. The greater the deflection of the shaft, the shorter is the useful life of the shaft. Additionally, this simply supported structure has a relatively limited area across which forces arising from the action of the transmission on the shaft-mounted sprockets and from the resistance applied by the rotary table and the cat shaft can act to produce excessive stress.
Therefore, there is the need for a new draw works which is constructed so that the magnitude of deflection of the shaft is reduced to thereby increase the life of the shaft. Additionally, there is the need for a new construction which reduces the stress in any one support member supporting the shaft.
Although there are these two needs, such a new construction should not limit the accessibility of clutches which are part of the draw works because the clutches are the elements which most often need to be replaced or repaired. The new construction also should be such that it does not significantly increase the manufacturing cost of the draw works whereby the new draw works is competitive with the prior type of draw works.
Still further, such a new construction should meet the reduced deflection and stress needs by utilizing support structures which will increase the tensile resistance to pull and which will provide a stronger draw works.
To facilitate the maintenance of the new draw works, it should also be designed to utilize standard bearings.